1. Field of the Invention
The present invention relates to a method of estimating the volume of a pressurized gas tank.
The invention may especially be used in a station for filling bottles or tanks with pressurized gas.
Advantageously, the invention may be applied in stations for filling vehicles with gaseous fuel (especially hydrogen).
2. Related Art
Stations for filling gas tanks for motor vehicles powered by hydrogen are generally adapted to one or more defined types of tanks to be filled.
This is because it is important to know the volume of the tank to be filled in order to achieve optimized filling, safe from the point of view of safety.
In addition, it is generally not possible or not appropriate to measure the pressure and the temperature inside the tank.
Document WO 2005/080201 A1 describes a filling station that estimates the initial gas density in a tank by means of a preliminary pressure measurement and an injection of gas of defined amount. The density is estimated via a model based on regression equations. The station described in that document also estimates the volume of the tank at two different times: two streams of gas are injected and, each time, the pressures are measured and compared with reference pressure ramps in order to estimate the volume of the tank.
Moreover, this known station controls the filling only by the mass of gas transferred.
However, the volume estimated using this method has drawbacks. Apart from the fact that it is necessary to carry out two gas injections and two estimates in succession, according to this method the volume is estimated by comparing the estimated density with tables expressing the volume as a function of reference density curves.
In addition, the gas density estimated according to the above document does not enable the quantity of gas in the tank to be known with sufficient precision. Thus, the initial level in the tank is determined indirectly. This requires knowing in advance the type of tank (volume, material) so as to be able to choose this reference. Moreover, the initial quantity of gas (in number of molecules) is not calculated.
Document EP 1 693 611 A2 describes a filling station that determines the gas density in the tank by a direct measurement in the tank. This method has the same drawbacks as those discussed above (inappropriate measurements in the tank). According to the above document, filling requires the volume of the tank to be known. Thus, this method cannot be used for a tank of unknown volume.